IP phone 7940 constantly rebooting after swapping router

Unanswered Question
Oct 22nd, 2009


Not quite sure if this is the right group but we are experiencing some weird issues with the VoIP phones after swapping out a 1700 series router with a newer 2821 router.

What is happening is that the 7940 phones keep rebooting or just not allowing users to answer a ringing phone.

The configuration is the same on the new router as the old router and there are no errors reported by the router or switches.

Any ideas on why this may be happening?

On the original 1760 router there were no problems.

Also upgraded the IOS on the 2821 to the latest version and that didn't seem to help.


- Trevor

I have this problem too.
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tajennings Thu, 10/22/2009 - 07:10


Thanks for the reply.

What do you think would be causing the phone FW to be conflicting with the router IOS?


- Trevor

Paolo Bevilacqua Thu, 10/22/2009 - 07:16

CME is like that. You should observe the boot phone process and determine what makes it fail.

tajennings Thu, 10/22/2009 - 07:34

Problem is that the phone boots fine and the issue is intermittent.

Seems sometimes that the phones will work fine and at random the phones reboot or a call not be able to be answered.


- Trevor

Paolo Bevilacqua Thu, 10/22/2009 - 07:37

Probably old buggy phone FW and you should upgrade it.

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tajennings Thu, 10/22/2009 - 10:10

Well we upgraded the phones as we were in fact using the older model and FW.

But now it seems that everynow and then the phones will re-register to the network (No rebooting so far).

tajennings Fri, 10/23/2009 - 11:53

Nope no rogue DHCP servers on the wire.

Just found out this afternoon that the phones will seem to lose connection to the call manager and display something like "cm fallback service operating" and no dial tone so basically have to do a reboot on the phone to get it to re-connect to the CM.

Could be that the connection is over a wireless bridge? But that doesn't make sense as the phones were working fine with the 1760 router.

tajennings Fri, 10/23/2009 - 12:40

On the 2821 router we are using 12.4.25b and on the VoIP phones, using FW SCCP41-8-4-3S.

tajennings Fri, 10/23/2009 - 12:56

The phones are 7941. If you are refering to the call manager version, we are using CUCM 7.0(2)

Paolo Bevilacqua Fri, 10/23/2009 - 13:07

Are the phones on a different subnet than the CM ? What is the physical setup ?

Are you using DHCP server, if so where ?


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